Current ink jet printing systems consist of a fluid system supporting one or more printheads. Typical ink jet printheads operate by forcing fluid through a droplet generator that contains an array of orifices, forming droplets of ink. The printhead is fully supported by the fluid system. The fluid system controls different valves and pumps to perform necessary functions for the printhead to operate reliably. These functions include cleaning, startup, and shutdown. One particular function, shutdown, provides a means to stop the operation of the printhead and fluid system over an extended period of time and, allows for a restart of the operation. If ink or cleaning fluid is left in the droplet generator, the fluids can dry in and around the orifices leaving behind non-volatile components in the form of solids or gels. Upon subsequent startups, the failure to remove or re-dissolve all of this material in and around the orifices creates disturbances in the shape or direction of the emerging jets.
McCann U.S. Pat. No. 5,463,415 describes one operation of shutting down a printhead of an ink jet printing system. Shutdown consists of applying a high vacuum to the outlet of a droplet generator with the inlet open to the atmosphere through a filtered restriction. Air is drawn into the droplet generator through a filtered restriction, and through the droplet generator orifices, to remove the ink from the interior of the droplet generator. Problems arise with the method in the McCann reference when air flow rates are insufficient to remove significant amounts of ink from the droplet generator of very large arrays of jets.
Enz U.S. Pat. No. 6,679,590 teaches pulsing air flow to dry the printhead.
Loyd U.S. Pat. No. 6,352,339 teaches a vacuum system which is used to clean ink jet printers. The prior art described herein are incorporated by reference.
A need exists for a shutdown procedure that effectively removes ink from the drop generator and orifice structure without causing particles to be deposited around the orifices and without using a vacuum or pulsed system.